Such a kind of a steering angle sensor is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-29158, and FIG. 1 is a diagram illustrating a steering system of a vehicle. In this diagram, a steering angle sensor 101 operates simultaneously with a steering wheel 102 in a rotational ratio of 1:1, and an output signal from the steering angle sensor 101 as well as a signal from a wheel velocity sensor 103 for detecting a wheel velocity, a signal from a yaw rate sensor 104 for detecting a yaw rate, a signal from a steering ratio sensor 105 for detecting a steering ratio, a signal from an ignition (IG.) switch 106 and the like is connected to a control unit 107. A steering angle range which is covered by the output signal from the steering angle sensor 101 is divided into three zones: a neutral zone in a predetermined range including at least a neutral position; a right zone; and a left zone adjacent to the neutral zone where output signals from the steering angle sensor 101 show the same value. A determination is made which zone a current steering angle is in based on a velocity difference between right and left wheels, a yaw rate and a vehicle velocity.
The control unit 107 sets a steering angle of a steering wheel based on the signals from the respective sensors and controls an operation of a steering ratio variable mechanism 109 that controls a steering ratio of wheels 108, so that a rear wheel steering mechanism 112 which is linked with a front wheel steering mechanism 111 via a transmission shaft 110 controls the steering angle of rear wheels.
In the steering system disclosed in Japanese Patent Application Laid-Open No. 8-29158, however, since information other than the steering angles, namely, information about the difference in wheel velocity, the yaw rate and the vehicle velocity is necessary in order to detect a rotational angle of the steering wheel, if these pieces of information have an error or abnormality, the determination as to the zone cannot be definitely made. Further, the determination as to the zones cannot be made unless initialization of the information is finished.
Therefore, it is an object of the present invention to provide a steering angle sensor in which a rotating cycle of a sensor wheel having a GMR element (Giant Magnetic Resistance) and a magnetizing portion arranged around the GMR element is improved and a range where a steering angle is detected using the GMR element is enlarged, so that accuracy of a steering angle estimation using the vehicle information can be low, a cost is low and an absolute steering angle can be detected quickly.